The present invention relates to an electron microscope with an electron spectrometer capable of acquiring an electron energy loss spectrum and a two-dimensional element distribution image and more particularly, to an electron microscope with a lens adjustment system capable of adjusting the electron spectrometer highly efficiently and highly accurately and to a lens adjustment method as well.
With advancement of fineness of working dimensions of a silicon semiconductor, a magnetic device and the like and with advancement of their high-grade integration, problems of degradation in device characteristics and reduction in reliability have now become more serious than heretofore in the course of developing a new process and of a mass production process. In recent years, for the purpose of getting to the root of causes of the faults as above, a spectroscopic analysis/two-dimensional distribution analysis based on electron energy loss spectroscopy (EELS) using a transmission or (scanning) transmission electron microscope ((S) TEM) has become an indispensable analytical means in analysis of faults of nanometer area in the semiconductor device and has been fulfilling itself in an analysis of faults in which the chemical reactions take part in the process development and mass production.
For the electron energy loss spectroscopy, electron energy loss observation equipment using an electron microscope and an electron spectrometer for energy dispersion in combination is employed. The electron spectrometer has the ability to acquire electron energy loss spectra and a two-dimensional element distribution by making use of an energy dispersion of an incident electron beam and a group of lenses such as multi-pole lenses to perform the enlargement/constriction of spectrum and the adjustment of focus.
Upon installing the electron spectrometer, a plurality of lenses inside the electron spectrometer are optimized for placing the energy resolution in good condition. But because of the lenses varying with time and the change of external disturbance near the apparatus, the electron spectrometer is not always used in the optimal condition.
As a solution to the aforementioned problem, JP-A-2003-151478 discloses a trial expedient according to which the magnetic field intensity of a multi-pole lens is changed every observation of an electron energy loss spectrum in such a way that the optimal condition of the electron spectrometer satisfies either a condition of minimization of the half-width of a peak due to a zero-loss spectrum or a condition of maximization of the intensity of a peak of a zero-loss spectrum, or both, and then optimization of the energy resolution is managed to be attained with the help of changed magnetic field intensity.
JP-A-2000-285845 also discloses a trial expedient in which with a view to efficiently adjusting the mechanical position of a spectroscope and the projection lens as well, a wobbler circuit that generates a wobbler signal of predetermined amplitude and frequency is provided and the spectroscope mechanical position and the projection lens are adjusted on the basis of an image shift or a defocus taking place when the spectroscope exciting current is increased/decreased with the help of the wobbler signal.